Encapsulating transformers with phenolic resin coated filler is well known, and taught by Hodges et al. in U.S. Pat. No. 3,161,843. In some advanced transformers, polyethyleneterephthalate (PET) film, is used for insulating purposes, such as for turn and phase insulation between electrical conductors, and is either in contact with the phenolic resin coated filler encapsulant or in the same transformer enclosure.
Experience with such PET-phenolic resin coated filler systems has disclosed, in some instances, brittleness of the PET insulating films, even where the PET film was not contiguous to the phenolic resin present. What is needed is a method to utilize such PET-phenolic systems without degradation of the polyethyleneterephthalate.